Pd(II)-N-heterocyclic carbene complexes of annelated ligand: Synthesis, characterization, and catalytic activity

The annelated imidazolium salt 1-methyl-2-(pyridin-2-yl)imidazo[1,5-a]pyridin-4-ylium hexaflurophosphate (1HPF6) has been synthesized by via formylative cyclization of the corresponding Schiff base 2-acetylpyridyl-N-(2-pyridyl)methylamine using standard conditions followed by anion metathesis with NH4PF6. Reaction of 1HPF6 with silver oxide and palladium chloride led to the formation of the palladium complex [Pd(1)2Cl]PF6, 2. Subsequent reaction of 2 with AgPF6 gave the palladiumcomplex [Pd(1)2][PF6]2, 3. The complexes have been fully characterized by different spectroscopic techniques and finally the solid state structures of 2 and 3 have been determined by single crystal X-ray diffraction studies. The catalytic activities of 2 and 3 have been tested in the Suzuki–Miyaura coupling reactions of several activated parafunctionalized aryl bromides with phenyl boronic acid to find that 2 is slightly more efficient than 3.